FIG. 1 illustrates a sand casting mold for casting metal parts. The sand casting mold is generally identified with the numeral 10. The illustrated mold 10 is formed in two complementary parts forming a mold cavity 12. The cavity 12 is surrounded by mold sand 14. Molten metal is poured into the cavity 12 through a mold sprue 16. One or more risers 18 are provided to permit air to escape from the cavity while the cavity is being filled and to provide a reservoir for molten metal while the metal in the cavity is cooling and contracting.
Refractory insular sleeves 20 are provided at the sprue 16 and riser 18 to protect the sand and to prevent sand from being carried into the cavity as the molten metal is being poured.
Considerable effort has been expended to develop insular riser/sprue sleeves that not only perform the traditional function of facilitating the pouring and uniform filling of a sand cast mold cavity with molten metal, but also filters the molten metal to remove foreign particles as the molten metal is being poured without materially hindering the flow of the molten metal into the mold cavity.
Several attempts have been made to construct such sleeves having filter systems mounted within the sleeves themselves. One such sleeve is commercially available under the brand name "Dypur" from Foseco, International Ltd. of Birmingham, England. It is generally described in U.S. Pat. No. 4,928,746 (Butler et. al.). The "Dupur" sleeve utilizes a rigid porous ceramic foam disc separately mounted to the interior wall of the insular sleeve to filter the molten metal as the metal flows through the sleeve into the sand cast cavity. Shoulder or wedge structures are utilized to rigidly secure the disc filter to the interior wall to minimize the possibility of the disc filter being dislodged and passing with the molten metal into the mold cavity, thereby ruining the casting.
Although the "Dupur" sleeve has met with some commercial success, it is rather expensive and has other disadvantages. Attempts have been made to place a less expensive circular flexible refractory mesh filter within an insular sleeve to perform the filtering function as well as providing a weakened fracture plane to facilitate the removal of the resulting metal sprue or riser after the molten metal has solidified.
One such prior attempt is illustrated in FIGS. 2-4. The sleeve 20 has a tubular wall 22 with outer and inner surfaces 24, 26 extending from an inlet end 28 to a reduced diameter (necked down) outlet end 30 (closest to the cavity 12). A refractory woven mesh filter 32 is mounted in the necked down outlet end 30. The filter 32 has a circular periphery 34 that projects into wall 22 more than one-half the thickness of the wall 20 at the outlet end 30. Such a penetration by the filter 32 materially weakens the strength of the wall 22 facilitating wall fracture. However, if the periphery of the mesh filter does not extend a sufficient distance into the wall, the filter is not adequately supported and the filter has a tendency to become partially or wholly dislodged from the wall and rendered ineffective.
One of the principal objects and advantages of the present invention is to provide an inexpensive sprue/riser sleeve having a woven mesh filter that does not materially weaken the sleeve wall while at the same time is unlikely to become partially or wholly dislodged from the wall from the combined head and flow pressure exerted by the molten metal as it passes though the sleeve into the mold cavity.
These and other objects and advantages of this invention will become apparent upon reviewing the attached drawing and following description of preferred and alternate embodiments.